The present invention relates generally to cooled rotor blade structures for gas turbine engines and more particularly to improved cooling for a turbine rotor blade utilizing vaporization and decomposition of an endothermic fuel.
In the operation of a gas turbine engine, the flow of gaseous reaction products from the combustion chamber of the engine is used to drive the turbine by passing the gaseous products against a plurality of turbine blades mounted on the turbine rotor. Temperature of the gaseous combustion reaction products contacting the turbine blades may be in excess of 2500.degree. F., and engine performance may be optimized in many applications by allowing a high operating temperature for the turbine inlet. In order to withstand these temperatures, hollow turbine blades have been used and cooled by flowing a coolant fluid, usually air, through the blades. To this end, existing turbine blade configurations have included hollow castings having internal air conducting chambers or passageways having suitable inlets and outlets through which coolant air may be passed.
The amount of cooling which may be provided to a turbine blade by air flow is, however, limited by the allowable air mass flow rate which can be diverted from the engine compressor, the heat capacity of the air, and the heat transfer coefficient at the interface of the air and the blade internal surfaces.
The invention solves or substantially reduces in critical importance problems with prior art turbine blade cooling methods and structures by providing cooling by vaporization and decomposition of an endothermic fuel. An endothermic fuel is a liquid fuel which decomposes in the presence of a catalyst into two or more gaseous compounds different chemically from the liquid, at least one of the gaseous compounds being combustible. An endothermic fuel is conducted to the interior of a hollow turbine blade and sprayed onto the interior wall surfaces of the hollow blade. The interior surfaces of the blade are coated with a catalyst. The fuel vaporizes and decomposes upon contacting the catalyst and thereby absorbs heat from the turbine blade wall. Fuel decomposition products flow along the blade wall toward the blade tip under the influence of centrifugal force, exit the blade through openings provided therefor and are collected for subsequent burning in the engine.